1. Field of the Invention
The present invention relates to a method of detecting abnormality of fuel injection and to a common rail fuel injection control system and particularly relates to improving the reliability of fuel injection control operation.
2. Description of the Related Art
The present invention pertains to a method of detecting abnormality of fuel injection and to a common rail fuel injection control system and particularly relates to improving the reliability of fuel injection control operation.
Common rail fuel injection control systems have come to be widely employed as systems that control the supply of fuel to internal combustion engines represented by diesel engines, but in recent years, from the viewpoint of realizing higher pressure and higher precision fuel injection control, there have been proposed systems of various configurations, such as a system using a piezo injector using a piezo element as a fuel control valve as disclosed, for example, in JP-A-2007-510849.
Incidentally, in these fuel injection control systems, there is disposed a return fuel passage for returning surplus fuel from fuel injection valves to a fuel tank, and in order to ensure that it does not inhibit injection operation of the fuel injection valves, a pressure holding valve is disposed in the return fuel passage, and the pressure on the return fuel passage side as seen from the fuel injection valves is held at a predetermined pressure or higher as disclosed, for example, in JP-A-2006-523793.
Disposing a pressure holding valve in the return fuel passage from the fuel injection valves is the same even in the system using a piezo injector mentioned previously. Particularly in the case of piezo injectors, piezo injectors employing a configuration where a hydraulic circuit is used in order to amplify the stroke of piezo actuators are common, but in terms of the structure thereof, a little fuel leaks from this hydraulic circuit to the aforementioned return fuel passage per one stroke of injection, so in order to refill with fuel for the next injection, it is necessary to reliably hold the pressure with the pressure holding valve interconnecting the piezo injectors and the return fuel passage.
However, it is common for the aforementioned pressure holding valve to have a mechanical configuration, and it is not the case that some kind of electrical control is applied from the outside, so when a fault arises and the pressure holding valve becomes unable to hold the predetermined pressure, sometimes this leads to injection abnormality such as described next, and that injection abnormality cannot be detected. That is, for example, in a state where the rail pressure is a relatively low pressure, when a fault arises where the pressure holding valve cannot hold the predetermined pressure, there are cases where, rather than fuel injection becoming completely unable to be performed, fuel injection is performed even though the injection quantity is lower than the normal injection quantity. In this case, fuel injection is still being performed even though there is a difference in the injection quantities, and it is not the case that the fault in the pressure holding valve itself is detected, so conventionally, the control system has been unable to determine this state to be one where the injection state is abnormal. In this manner, a phenomenon where fuel injection is performed in a state where the injection quantity has fallen lower than the normal quantity can similarly occur even when a mechanical fault has arisen in the fuel injection valves, and currently there is no technology that reliably detects that.